A unique number that ensures that the request can't be replayed. If the CallerReference
is new (no matter the content of the StreamingDistributionConfig object),
a new streaming distribution is created. If the CallerReference is a
value that you already sent in a previous request to create a streaming distribution,
and the content of the StreamingDistributionConfig is identical to the
original request (ignoring white space), the response includes the same information
returned to the original request. If the CallerReference is a value that
you already sent in a previous request to create a streaming distribution but the
content of the StreamingDistributionConfig is different from the original
request, CloudFront returns a DistributionAlreadyExists error.

A complex type that specifies any AWS accounts that you want to permit to create signed
URLs for private content. If you want the distribution to use signed URLs, include
this element; if you want the distribution to use public URLs, remove this element.
For more information, see Serving
Private Content through CloudFront in the Amazon CloudFront Developer Guide.